This invention relates to an ignition testing apparatus and particularly to such apparatus for dynamically analyzing the operation of capacitor discharge ignition systems.
Capacitor discharge ignition systems have been recently developed for operation of internal combustion engines. Generally, such systems employ a capacitor which is charged to a selected level and then selectively discharged to a spark plug for firing of the engine. The capacitor charging circuit may generally employ a battery and suitable D.C. to D.C. converter to charge the capacitor or, alternatively, may employ an engine driven alternator. A triggered blocking oscillator provides a highly satisfactory D.C. to D.C. converter, and preferably employs a solid state switching unit for initiating a charging cycle. The discharge circuit generally employs a control rectifier or other similar solid state threshold switching means for completing of a discharge circuit. A controlled rectifier and a pulsing transformer may be employed to provide for rapid transfer of the energy from the capacitor into the spark plug circuit.
A particularly satisfactory battery driven charging circuit employing a blocking oscillator is shown in U.S. Pat. No. 3,502,955 which issued Mar. 24, 1970 to F. Minks wherein the initiation of the charging cycle simultaneously establishes a discharge signal for firing of a control rectifier and discharging of the capacitor energy stored from a previous cycle. A saturable unit is provided to terminate the charging cycle and thereby transfer a predetermined constant amount of energy to the capacitor during each charging cycle to establish a closely regulated energy transfer per pulse to the spark plug.
The controlled rectifier of the discharge circuit is preferably actuated from a breakerless system. A preferred means includes a control oscillator which is switched on and off by a distributor driven apertured metal disc to generate successive pulses for simultaneously firing the controlled rectifier and triggering of the blocking oscillator circuit as more fully shown in U.S. Pat. No. 3,502,955.
Another satisfactory breakerless capacitor ignition system employs a magnetically driven differential amplifying circuit including a distributor driven rotating magnetic means to generate a series of triggering pulses as shown in U.S. Pat. No. 3,696,257 which issued Oct. 3, 1972 to Charles L. Shano. The pulse initiates operation of a charging circuit having a current level sensing resistor to provide for predetermined energy transfer to a capacitor. The trigger circuit is also connected to the input of the controlled rectifier to discharge the capacitor.
An alternator driven system may also take various forms. For example, U.S. Pat. No. 3,890,948, dated June 24, 1975, for "ALTERNATOR DRIVEN CAPACITOR POWER SYSTEM" discloses an alternator driven capacitor discharge ignition system wherein a dual winding alternator is provided for charging of a capacitor to a selected level at varying speeds, with one winding predominantly operating at a low speed range and the other winding predominantly operating during the high speed range. The capacitor is charged during one half-cycle of the alternator output and triggered during and in response to the negative half-cycle. Alternatively, a separate triggering alternator may be employed, particularly to provide a distributorless ignition. Thus, as shown in U.S. Pat. No. 3,566,188 which issued Feb. 23, 1971 to F. Minks, a separate trigger signal generator may be provided with separate triggering windings for connection to individual control rectifiers for selectively discharging of the capacitor energy into any one of a plurality of discharge circuits connected to corresponding individual spark plugs.
Further, particularly when the apparatus is applied to outboard motors and the like, the electronic circuitry is preferably potted in a suitable encapsulating plastic or the like to prevent damage to the components from the environment and also from vibration and the like. This, however, makes it extremely difficult to check the operation of the potted circuit.
Further, the capacitor discharge ignition systems as described employ electronic circuitry which requires significant knowledge and skill in electronics in order to properly evaluate the circuit. Generally, service personnel who have been servicing the more conventional breaker point system will not have the knowledge and skill to properly evaluate and service electronic ignition systems.
As a result, the servicing, maintenance and repair of an electronic ignition system has presented very significant practical problems and generally the switch units are returned to the factory if the service personnel determines that it is the ignition system that is preventing proper operation. Often, however, the system may be improperly evaluated because of the limited capabilities of the service personnel and the ignition failure improperly assigned to what is, in fact, a properly functioning unit.